Office chairs conventionally provide some type of rearward tilting movement. In its simplest variations, the rear tilting involves solely the back, or the seat and back as a unitary construction. To provide improved and more desirable tilting movement and seating comfort, however, many office-type chairs employ a synchrotilt mechanism coupled between the chair base and the seat-back assembly, for permitting the seat and back to simultaneously tilt at different rates, with the tilt rate and maximum tilt angle of the back typically being about twice the tilt rate and maximum tilt angle of the seat.
Chairs employing synchrotilt mechanisms for permitting simultaneous but relative tilting of the seat and back are well known, and numerous mechanisms have been developed for performing this function. Additionally, such synchrotilt mechanisms include a subassembly, namely a tilt tension mechanism that includes a resilient biasing arrangement which permits rearward tilting or reclining of the seat and back while generating a resilient restoring force to bias the seat and/or back upwardly or forwardly to a normal, unreclined position. Known biasing arrangements typically include a spring mechanism such as a coil spring or torsion bar which provide the resilient restoring force.
For those types of chairs having a torsion bar, such torsion bars typically include an arm projecting radially therefrom which is swingable circumferentially about an elongate axis of the torsion bar. This drive arm controls the deflection within the torsion bar, and as such, the amount of displacement of the drive arm controls the restoring force. Known chair arms have used various drive mechanisms for displacing the drive arm pursuant to a manual actuator that is controlled by the chair occupant.
For example, U.S. Pat. No. 5,772,282 (Stumpf et al.) discloses a driving arrangement having a upwardly extending threaded drive shaft which is rotatably mounted to a control body of the tilt tension mechanism. A block member engaged with the distal end of the radial arm of a torsion spring moves up and down the threaded shaft in response to rotation thereof. The mechanism of the '282 patent includes a bevel gear on the upper end thereof which cooperates with a cooperating bevel gear that meshes therewith and is driven by a rotatable handle.
The invention relates to a chair having an improved drive mechanism for driving the drive arm of a torsion bar by manual rotation of an actuator handle. The tilt tension mechanism of the invention includes a threaded drive shaft rotatably mounted on the control body of the tilt tension mechanism and a follower nut which rides vertically along the drive shaft in response to shaft rotation.
To drive the shaft, an improved gear drive arrangement is provided comprising a drive gear and a sidewardly-oriented actuator shaft having a pinion section with spiral threads thereon which mate with corresponding spiral gear teeth on the face of the drive gear. Rotation of the actuator shaft effects rotation of the drive gear, and the gear and pinion have a spiral teeth arrangement to provide continuous engagement between multiple teeth in an effort to reduce tooth stress and loading, reduce backlash and improve the overall operation of the gear drive.
Other objects and purposes of the invention will be apparent to persons familiar with constructions of this general type upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience in reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. These latter terms will also refer to the normal directions and positional orientations associated with a person sitting in the chair. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the chair and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.